The invention relates to polyolefin blends having superior physical properties including enhanced scratch resistance, rigidity, and toughness. The invention also relates to the process of manufacturing such polyolefin blends and to articles produced from such polyolefin blends.
In numerous applications, such as many in the automotive industry, a polymeric material that exhibits a good level of scratch resistance balanced with rigidity and impact toughness is desired. These properties tend to vary, however, such that efforts to enhance one will often result in deterioration of one, or both, of the others.
Polypropylene blends are useful in a wide variety of applications due to their strength, environmental resistance and processability. While highly crystalline polypropylene does exhibit good mar and scratch resistance, it does not possess the impact toughness required in many important applications such as the making of automobile parts. Special polymeric materials have been developed that can partially overcome this problem.
Attempts to remedy polypropylene""s deficiency in impact toughness by blending with impact modifying copolymers of ethylene and other alpha-olefins, terpolymers of ethylene, other alpha-olefins, and dienes have not been completely successful. Elastomer modified polypropylene blends, also known as thermoplastic polyolefins, have the advantage of improved toughness, especially for cold temperature impact. They are widely used for formed or shaped articles such as automotive parts, toys, furniture, and housing products. Although the impact toughness of those compositions is improved by these modifiers, the scratch resistance has been found to decrease. That is, the scratch resistance of polypropylene blends including impact modifiers such as ethylene-propylene copolymers, ethylene-propylene terpolymers, ethylene-butene copolymers, or ethylene-octene copolymers is poor.
Increasing the crystallinity of the polypropylene to obtain a harder surface, and/or adding hard mineral filler to these blends, has been attempted as a countermeasure without complete success. One conventional method to enhance surface characteristics is to use inorganic particulate material. Uniform dispersion of these particulates is difficult to achieve, however, and this results in non-uniform surface properties in such products. The use of these particulates also tends to damage other desirable physical properties of the polyolefin, resulting in loss of impact strength and/or toughness. Debonding of these particulates from the polyolefin system also contributes to undesirable stress whitening.
Another conventional way to enhance surface characteristics of various articles is to apply acrylic polymers or coatings to an article and subsequently cure the polymer or coating with a radiation source, such as ultraviolet radiation.
A method to enhance surface characteristics of polyolefins is described in U.S. Pat. No. 4,000,216, which discloses an extrudable, moldable, or heat formable blend of a thermoplastic polymer and a surface altering agent of at least one monoethylenically unsaturated monomer for said thermoplastic polymer, wherein the surface altering agent has cross-linked polymer particles having an average size of 1 to 30 microns. The surface altering agent is preferably prepared by an endopolymerization, which is used with a compatible polyolefin to be altered.
European Patent Application 0794225A1 describes thermoplastic resin compositions comprising polypropylene, a styrene containing elastomer, and talc, and having an acceptable balance of toughness and rigidity. The disclosure stresses the importance of the proportions of each component used to achieve this balance. In PCT Application WO97/38050, a similar balance of properties is reported for a thermoplastic resin comprising an ethylene-propylene based polymer composition, an ethylene/alpha-olefin copolymer based rubber and/or a rubber containing vinyl aromatic compounds and talc. Another example of a composition that provides an acceptable balance of toughness and rigidity is reported in Japanese Patent Application 10219040A for a resin composition consisting of a polyolefin based resin and a block copolymer based on aromatic vinyl and butadiene monomer units. Polymer blends which can be formed or shaped into lightweight and durable articles useful, for example, as automobile parts, toys, housings for various types of equipment, and the like, are well known in the art.
The physical and/or chemical properties of the thermoplastic polyolefin blends can be modified either by blending them with other thermoplastic polymers, or by incorporating into them materials having one or more polar groups, or both. For example, U.S. Pat. No. 4,946,896 describes a thermoplastic polyolefin comprising 20-80 weight percent polypropylene; 5-38 weight percent of an ethylene copolymer consisting of ethylene, an ester unit of either alkyl acrylate or methacrylate, and an unsaturated dicarboxylic acid anhydride; and 5-70 weight percent ethylene-propylene rubber. Similarly, U.S. Pat. No. 4,888,391 describes a polyolefin composition comprising a blend of a polyolefin as the continuous phase with an ethylene/acrylate/acrylic acid terpolymer as a discontinuous phase. These polyolefin-based blends are paintable.
Despite these prior art formulations, there remains a need to obtain polymeric materials that have a good level of mar/scratch resistance along with the physical property requirements of rigidity, strength, processability, and low temperature impact toughness required for various applications. The present invention provides certain blends that meet these needs.
The present invention encompasses a polyolefin blend including from about 1 to 99 weight percent of a propylene-based polyolefin-metal salt that is a reaction product of a propylene-containing polymer functionalized with a first hydrophilic moiety and at least one metal ion present in an amount sufficient to at least partially neutralize the first hydrophilic moiety, and from about 1 to 99 weight percent of an ethylene-based polyolefin-metal salt that is a reaction product of a copolymer of ethylene functionalized with a second hydrophilic moiety and at least one metal ion present in an amount sufficient to at least partially neutralize the second hydrophilic moiety.
In one preferred embodiment, the propylene-based polyolefin-metal salt can include from about 25 weight percent to 80 weight percent of the blend and the ethylene-based polyolefin-metal salt comprises from about 5 weight percent to 60 weight percent of the blend. In another preferred embodiment, the propylene-based polyolefin-metal salt includes from about 30 weight percent to 65 weight percent of the blend and the ethylene-based polyolefin-metal salt comprises from about 20 weight percent to 55 weight percent of the blend and wherein the blend optionally further includes from about 5 to 50 weight percent of at least one of a propylene-containing homopolymer or copolymer.
In one embodiment, the first and second hydrophilic moieties each include an ethylenically unsaturated carboxylic acid monomer. Preferably, the first and second hydrophilic moieties can each independently include methacrylic acid, acrylic acid, maleic anhydride, or a mixture thereof.
In one embodiment, the polyolefin blend further includes a semi-crystalline propylene-containing polymer in an amount of up to 50 weight percent. In a preferred embodiment, the semi-crystalline propylene-containing polymer is present in an amount of about 5 to about 45 weight percent. In yet another embodiment, the polyolefin blend further includes a semi-crystalline propylene-containing polymer in an amount of greater than 50 to about 80 weight percent.
The polyolefin blend can further include about 1 weight percent to 20 weight percent of a copolymer of ethylene and an alpha-olefin, at least one of which is functionalized with a third hydrophilic moiety. In one preferred embodiment, the alpha-olefin includes at least one of propylene, 1-butene, 1-hexene, 4-methyl-1-pentene, 1-heptene, 1-octene, and mixtures thereof, and the copolymer is at least partially neutralized with at least one metal ion. In another embodiment, the polyolefin blend further includes a toughening component in an amount of up to about 40 weight percent, the toughening component comprising semi-crystalline or random copolymers of ethylene and an alpha-olefin, and optionally at least one diene. In a preferred embodiment, the diene is nonconjugated and includes at least one of straight chain dienes; cyclic dienes; or bridged cyclic dienes. In a more preferred embodiment, either the straight chain diene is present and includes 1,4-hexadiene, the cyclic diene is present and includes at least one of cyclooctadiene or dicyclopentadiene, or the bridged cyclic diene is present and includes ethylidene norbornene, or a combination thereof.
The polyolefin blend can further include an interfacial modifier of a styrenic block copolymer, a random styrenic copolymer, or mixtures thereof, present in an amount of about 0.1 to 40 weight percent of the polyolefin blend. In one embodiment, the styrenic block copolymer includes styrene-butadiene, styrene-butadiene-styrene, styrene-butene-butadiene-styrene, styrene-isoprene, styrene-isoprene-styrene, alpha-methylstyrene-butadiene-alpha-methylstyrene, alpha-methylstyrene-isoprene-alpha-methylstyrene, styrene-(ethylene-butene)-styrene, styrene-(ethylene-propylene)-styrene, styrene-(ethylene-butene), styrene-(ethylene-propylene), styrene-butene-styrene, styrene-butene, hydrogenated variations thereof, or combinations thereof. In another embodiment, the random styrenic copolymer of ethylene and styrene has a blocky comonomer distribution.
The polyolefin blend can also include a mineral filler, which is typically present in an amount from about 1 to 40 weight percent of the polyolefin blend. In another embodiment, the filler is present in an amount of about 1 to 25 weight percent. In one embodiment, the mineral filler can include at least one of talc, calcium carbonate, wollastonite, alumina trihydrate, barium sulfate, calcium sulfate, carbon blacks, metal fibers, boron fibers, ceramic fibers, polymeric fibers, kaolin, glass, ceramic, carbon or polymeric microspheres, silica, mica, glass fiber, carbon fiber, clay, or mixtures thereof.
The metal ion(s) included in the polyolefin blend include at least one of lithium, sodium, potassium, magnesium, calcium, barium, lead, tin, zinc, aluminum, or mixtures thereof.
The invention also encompasses articles including the polyolefin blends above, as well as methods of preparing such articles. One such method of preparing an article according to the invention is by melt blending a propylene-based polyolefin-metal salt that is a reaction product of a propylene-containing polymer functionalized with a first hydrophilic moiety and at least one metal ion present in an amount sufficient to at least partially neutralize the first hydrophilic moiety, and an ethylene-based polyolefin-metal salt that is a reaction product of an ethylene copolymer functionalized with a second hydrophilic moiety and at least one metal ion present in an amount sufficient to at least partially neutralize the second hydrophilic moiety, so as to form a blend, wherein the melt blending is at a sufficiently high temperature so that each polymer is at least partially melted, and molding the blend into an article having an external surface, wherein the surface of the article when subjected to a 20 Newton load has less than about a 2.5 on the scratch rating scale and has no ribbing or tearing.
The method of providing propylene-based polyolefin-metal salts may include the steps of contacting a propylene-containing polymer and an organic monomer including a hydrophilic moiety under conditions such that propylene polymers are functionalized with the hydrophilic moiety, which is then neutralized with metal ions to form a reaction product. Similarly, the method of providing ethylene-based polyolefin-metal salts may include the steps of contacting a ethylene-containing polymer and an organic monomer including a hydrophilic moiety under conditions such that ethylene polymers are functionalized with the hydrophilic moiety, which is then neutralized with metal ions to form a reaction product. The reactive blending may be done in an extruder. The step of neutralizing the reaction product with metal ions may be done approximately simultaneously with the step of blending the components in a twin screw extruder. The process of contacting a propylene-containing polymer and contacting a ethylene-containing polymer with an organic monomer including a hydrophilic moiety under conditions such that propylene and ethylene polymers are functionalized with the hydrophilic moiety may be performed in a single reaction mass.